Art of mounting piezoelectric crystals



March'30, 1943. s. A. BOKOVOY 2,315,392

ART-OF MOUNTING PIEZOELECTRIC CRYSTALS Filed July 5, 1941 3nventorattorney Patented Mar. 30, 1943 ART OF MOUNTIN CRYS o rmzonmc'rmc TALSSamuel A. Bokovoy, Audubon, N. 1., assignor to Radio CorporationDelaware of America, a corporation of Application July 5, .1941, 'SerialNo. 401,102

Claims.

This invention relates to the art of mounting piezoelectric crystals andparticularly to improvements in so-called shock proof mountings for suchvibra'tile elements.

In mounting a piezoelectric crystal for use in aircraft 'and otherinstallationsofthe type normally subjected to shocks and tremors -ofappreciable magnitude, the usual practice has been to apply acompression force to the crystal as by means of a pair of clampsarranged to grip the crystal usually at those selected surface: pointsor areas which are known to give rise to the least possiblevibration-damping effect. In such cases some damping is to be expectedand can be tolerated within limits provided the clamping force isconstant and not variable, since in the latter case suddenrjumps orgradual shifts in the operating frequency of the crystal may take place.

As a practical matter, it is difficult to prevent changes in frequencyin crystal installations of the general character described. This.

is so because, usually, the surfaces of the crystal are as flat andsmooth as it is possible to make other hermetic closure since in thisevent neither the mount nor the crystal is accessible for purposes ofinspectionand repair.

The foregoing and other less apparent objections to prior art methods ofmounting Diem-- electric crystals are substantially overcome, inaccordance with the present invention, by subjecting the crystal in anovel manner to tension or to a stretching force, instead of to theusual vertically applied compression or clamping force. Certain detailsof construction together with other objects and advantages will beapparent and the invention itself will be best understood by. referenceto the following specification and to the accompanying drawing, wherein:

Figure l is a side elevational view of a metalized crystal having adished electrode face and mounted under tension, inaccordance with theprinciple of the invention;

Figure 2 is a fragmentary side elevational view force of the springs Sand S,

' mounting elements or jaws J and J and Fig. 3 a fragmentary sectionalview of a crystal support showing alternative means for subjecting adished crystal to tension;

Figure 4 is a sectional view showing one means of applying the inventionto a crystal having flat'and parallel electrode faces; and I Figure 5 isa front elevational view of a piezoelectric crystal mounted inaccordance with the invention and contained in a hermetically sealedcasing. v

In Fig. 1," P designates generally a quartz piezoelectric crystal havinga substantial flat "bottom major face and a top" major face which isdished outwardly from its center to provide a rim r, r along opposite ofits end zones or surfaces. The particular crystal illustrated comprisesa so-called V-cut crystal; its length thus lies along a Z+0 axis, itswidth along a Y+0 axis and its thickness dimension along an X+0 axis.The invention, however, is not limited in its useful application tocrystals of the above described orientation. The two necessaryelectrodes are in the form of adherent metal coatings or films e and 2'each of which partially covers both major faces of the crystal.

In accordance with the invention the crystal P is subjected to tensionor to a stretching force (instead of to the usual vertically appliedcompression or clamping force) as by means of 1 two springs S, S,respectively, which are anchored at one end to suitable immovablesupports A, A", and are secured at their opposite ends to inflexiblejaws J, J which engage the "flat bottom face and the upturned edges orrims r, 1'', respectively, on the metalized major top face of thecrystal. The laws J and J which engage the rims r, r of the crystal arepreferably constituted of an inflexible metal and, since they are urgedoutwardly by the biasing they subject the crystal to substantiallyconstant tension without danger of their being .pulled outwardly overthe upturned edges r, 1''. These separate c-shape may extend across thecrystal and are applied to the thinnest or dished parts thereof and thenmoved outwardly to contact the rims 1", r'. In the alternative form ofmounting element shown in Fig. 2 the tensioning force is applied to thecrystal P through one or more metal screws 0 which are shown threaded inone of the arms of the support J and contact the metalized rim rof thecrystal in a direction substantially normal to the inner face of thesaid rim. As in the previous described embodiment of the invention thesubstantially c-shape mounting elements J may exopposite arm of the C isprovided with a bend b so that it contacts the metalized flat bottomfaceof the crystal along a narrow line.

Referring particularly to Fig. 3: In some cases, as where theinstallation may be subjected to shocks tending to cause lateralmovement of the crystal P in its holders J, one or more retainingmembers may be provided to prevent such displacement. The retainingmembers or member may be in the form of a pin n mounted in or ,on thetensioning element C and extending into a hole or recess 72., providedfor the pu p se, preferably in the rim r of the crystal.

Fig. 4 shows one method .of applying a tensional supporting force to acrystal P having duplicate flat, parallel electrode faces. In this casethe crystal is provided with'one or more holes or recesses adjacent theopposite end zones of the crystal and which preferably extend into thecrystal in a direction normal to its major faces. comprisetheelectrodes, for the crystal cover the inner surface or walls of therecesses o and 0 thus make contact with the tensioning springs S and Swhich, as shown, extend into or through the said recesses or holes.

Where, as shown in Fig. 5, the crystal and its support are mounted in ahermetically sealed envelope E, the springs S and S which supply thetensioning force for the crystal P may be anchored either to the wallsor the envelope or to auxiliary conductive supports A, A adjacent theopposite ends of the envelope and which are connected as by leads m toprongs g, on its base. To prevent twisting or turning of the crystal twotensioning springs B may be provided preferably adjacent one of itsend-zones.

Other embodiments and modifications of the invention will suggestthemselves to those skilled in the art. It is to be understood thereforethat the foregoing is to be interpreted as illustrative and not in alimiting sense except as required by the prior art and by the spirit ofthe appended claims.

The metal coatings e and e which I of said crystal.

What is claimed is:

1. Method of mounting a piezoelectric crystal which comprises subjectingsaid crystal to tension applied at spaced points adjacent the surfacethereof.

2. Method of mounting a piezoelectric crystal which comprises subjectingsaid crystal to tension applied adjacent opposite end zones of saidcrystal.

3. Method of mounting a piezoelectric crystal which comprises subjectingsaid crystal to tension applied to the electrode faces of said crystal.

4. Method of mounting a piezoelectric crystal which comprises subjectingsaid crystal to tension applied at spaced subsurface areas in the bodyof said crystal.

'5. Method of mounting a piezoelectric crystal which comprisessubjectinl said crystal to tension applied to said crystal at theminimum number of points required to define the plane 6. In combination,a piezoelectric crystal, and means for applying a tensional supportingforce to said crystal at spaced points adjacent the surface thereof.

7. In combination a piezoelectric crystal having a raised portion on anelectrode face adjacent opposite ends thereof, and means for apply ing atensional supporting force to said raised portions of said crystal.

82 In combination, a piezoelectric crystal having a; recess adjacentopposite ends thereof, and means within said recesses for applying atensional supporting force to said crystal.

9. A holder for a piezoelectric crystal comprising, a support, andspring means on said support for applying a tensional supporting forceto said crystal.

10. A holder for a piezoelectric crystal comprising means for applying atensional supporting force to said crystal at the minimum number ofpoints required to deflne' the plane of said

